1. Field of the Invention
The present invention generally relates to a sheet processing device and an image forming system that includes the sheet processing device and an image forming apparatus.
2. Description of the Related Art
Devices, which are called as sheet processing devices, that automatically perform sheet processing such as alignment, stapling, and/or punching on sheets on which images are formed have been widely known. Image forming systems that include an image forming apparatus and this type of sheet processing device connected to the downstream of the image forming apparatus are widely used in recent years. Such a sheet processing device performs sheet finishing, e.g., stacking and stapling. Stacking is a process of stacking sheets on an eject tray while sorting the sheets into sets of sheets. Stapling is a process of stapling each sheet bundle made up of a predetermined number of sheets and stacking the sheet bundles on a stack tray.
Known examples of this type of technique are disclosed in Japanese Patent Application Laid-open No. 9-175724 and Japanese Patent Application Laid-open No. 2007-31095. Specifically, Japanese Patent Application Laid-open No. 9-175724 discloses a sheet finisher that receives printed sheets ejected from an image forming apparatus and distributes the sheets onto a plurality of bins and staples each sheet bundle on the bins. The sheet finisher includes a chuck device that advances toward a trailing-edge center portion of the sheet bundle distributed on one of the bins, chucks the trailing-edge center portion, and conveys the sheet bundle to a stapler located to the rear of the bin. The chuck device performs this operation for each of the bins. The chuck device includes a chucker that clamps the trailing-edge center portion of the sheet bundle loaded on the inclined bin and a moving unit that moves the sheet bundle clamped by the chucker to the stapler disposed on a downstream extension of the sheet bundle.
Japanese Patent Application Laid-open No. 2007-31095 discloses a sheet finisher that performs postprocessing on sheets. The sheet finisher includes a hole puncher (lateral-hole punching unit) that punches holes for use in sheet binding (hereinafter, “binding holes”) in predetermined positions of sheets. The hole puncher, which is movable, moves to binding-hole positions and punches the binding holes. According to this technique, a line connecting the binding holes punched by the lateral-hole punching unit is parallel to a sheet conveying direction. The lateral-hole punch, which is movable, moves to the binding-hole positions and punches the binding holes.
However, the technique disclosed in Japanese Patent Application Laid-open No. 9-175724 is disadvantageous in that the sheet bundle is not moved up and down. This is because although the sheet bundle clamped by the chucker is movable in a conveying direction, the sheet bundle is unmovable in the vertical direction. The sheet finisher disclosed in Japanese Patent Application Laid-open No. 2007-31095 has disadvantageously complicated structure to allow the punching unit to move when punching the binding holes. In addition, a large driving source is necessary to move the punching unit.
Therefore, there is a need to provide a sheet processing device capable of moving sheets with a simple structure without using a large driving source, thereby achieving miniaturization.